Petrogenesis of spilite and keratophyre from a Permian and Triassic volcanic arc terrane, eastern Oregon and western Idaho, U.S.A.

1978 ◽  
Vol 15 (8) ◽  
pp. 1356-1369 ◽  
Author(s):  
T. L. Vallier ◽  
Rodey Batiza
Keyword(s):  
Mass Balance ◽  
Ion Mobility ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Internal Mass ◽  
Volcanic Arc ◽  
Sea Floor ◽  
General Internal ◽  
Low Potassium

Spilite, keratophyre, and quartz keratophyre from a Permian and Triassic volcanic arc assemblage in eastern Oregon and western Idaho originally were low-potassium basalt, andesite, dacite, and possibly rhyolite. Amphibolite from an abyssal sea floor or marginal basin environment of either Permian or Triassic age originally was low-potassium basalt. Present mineralogies are characteristic of the greenschist and amphibolite facies of regional metamorphism. Greenschist facies minerals are mostly albite, epidote, chlorite, calcite, and quartz, whereas amphibolite facies minerals are predominantly hornblende, plagioclase (andesine), and epidote. In the volcanic arc assemblage, mineralogies of the Permian rocks are nearer equilibrium in the greenschist facies than those of the overlying Triassic rocks, probably reflecting deeper burial. Bulk compositions indicate extensive ion mobility, but there has been a general internal mass balance of most components. Na2O, CO2, and H2O were probably added to most rocks, but the source of those components has not been established.

METAMORPHISM OF THE MEGUMA GROUP OF NOVA SCOTIA

1966 ◽  
Vol 3 (7) ◽  
pp. 959-974 ◽  
Author(s):  
F. C. Taylor ◽  
E. A. Schiller
Keyword(s):  
Nova Scotia ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Contact Metamorphism ◽  
Granitic Rocks ◽  
Structural Elements ◽  
Early Ordovician ◽  
Quartz Veins ◽  
Granite Emplacement

The Meguma group of lithic greywacke, feldspathic quartzite, slate siltstone, and argillite is Early Ordovician or older in age and has undergone both regional and contact metamorphism. Both types of metamorphism have resulted in recrystallization and locally in orientation of newly formed minerals. Metasomatism and retrogressive metamorphism are subordinate and only locally important. Regionally metamorphosed rocks are divided into greenschist and almandine–amphibolite facies, although some assemblages cannot be assigned with certainty. Locally, biotite and garnet isograds are mappable within the greenschist zone.Relationships between regional metamorphism and structural elements (folding) show that deformation preceded regional metamorphism. Intrusion of granitic rocks has produced a zone of contact metamorphism (hornblende–hornfels facies) that is superimposed upon regional greenschist facies rocks, which shows that granite emplacement occurred after the regional grade was reached. Gold–quartz veins are confined to areas lying in the greenschist zone of regional metamorphism, which suggests that the almandine–amphibolite zone is not favorable.

In situ U-Pb geochronology on garnet and rutile: New age data from the Palaeoarchaean Onverwacht Group, Barberton Greenstone Belt, South Africa.

2020 ◽  
Author(s):  
Valby van Schijndel ◽  
Kathryn Cutts ◽  
Gary Stevens ◽  
Cristiano Lana ◽  
Thomas Zack
Keyword(s):  
Greenstone Belt ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Ongoing Research ◽  
Barberton Greenstone Belt ◽  
Garnet Core ◽  
Peak Metamorphism ◽  
Zr In Rutile

<p>The Barberton Greenstone Belt (BGB) is a well-preserved remnant of Paleo- to Mesoarchean crust. The oldest supracrustal rocks of the BGB consist of the 3.5-3.3 Ga Onverwacht Group. These rocks form a NE-SW trending belt deformed and metamorphosed largely under lower greenschist-facies conditions. In the southern BGB, the Komati Fault separates the structurally uppermost, lower greenschist-facies Onverwacht Group from its stratigraphically lowest components – the Sandspruit and Theespruit Formations (hereafter referred to as Lower Onverwacht Group), which occur south of the Komati Fault and have been metamorphosed under high-pressure amphibolite-facies conditions. The Lower Onverwacht Group rocks occur as a band along the southern edge of the greenstone belt and as septa between several ca. 3.55, 3.45 and 3.23 Ga Tonalite-Trondhjemite-Granodiorite plutons. The Lower Onverwacht Group rocks record a complex history of metamorphism and retrogression. An early phase of amphibolite-facies metamorphism is recorded at ca. 3.44 Ga by monazite in metasediments, whilst the main phase of the regional metamorphism occurred at ca. 3.23 Ga (e.g. Cutts et al., 2014).</p><p>The rocks targeted in this study have felsic metavolcanic protoliths and occur as a greenstone remnant within deformed and undeformed phases of 3.45 Ga Trondhjemites. They contain cm-sized garnets and the mineralogy of the samples indicate amphibolite-facies peak metamorphism. The garnets show major element growth zonation from core to rim (Alm<sub>0.63-0.80 </sub>Grs<sub>0.15-0.08</sub>Pyr<sub>0.0.05-0.09</sub>Sps<sub>0.17-0.0.03</sub>). U-Pb rutile geochronology gives an age at 3.15 Ga and Zr-in-rutile thermometry yields a temperature of ca. 640 °C (at 5 kbar). The rutile grains contain small, pristine zircon inclusions and the rutile is assumed to have grown in equilibrium with both zircon and quartz as buffer phases. The amphibolite-facies assemblage and the Zr-in-rutile temperature indicate that the rutile dates are cooling ages, which are difficult to interpret without information on the age of peak metamorphism of the samples. The objective of this study is to attempt to elucidate the early metamorphic record of these samples by directly dating the large garnet grains using in situ U-Pb laser-ablation inductively-coupled-plasma mass-spectrometry geochronology. Ongoing research shows that low-U garnet is datable by this method (Albert Roper et al., 2018). Preliminary results have been obtained from a different Lower Onverwacht Group sample, yielding a 3.45 Ga age for the garnet core and a 3.22 Ga age for the garnet rim (Cutts et al, unpublished data). The results indicate that U-Pb in rutile and in garnet from Archaean greenstones can be used in order to date metamorphic events. This is especially relevant when other potential datable accessory minerals, such as zircon or monazite, are not present.</p><p> </p><p>References</p><p>Cutts et al., 2014. Geological Society of America Bulletin 126, 251–270.</p><p>Albert Roper et al., 2018. Goldschmidt Abstracts, 2018, 32.</p>

Amphiboles and biotite in relation to the stages of metamorphism in granogabbro

1974 ◽  
Vol 39 (308) ◽  
pp. 857-866 ◽  
Author(s):  
W. Smulikowski
Keyword(s):  
Thermal History ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Low Grade ◽  
Chemical Changes ◽  
Grade Metamorphism ◽  
Facies Metamorphism

SummaryThe Bratteggdalen granogabbro, a relict mass in the Caledonian amphibolites of Vestspitsbergen, shows a series of amphibole development reflecting its thermal history. A brown Ti-rich hornblende occurs as a late magmatic mantling of pyroxene. Low-grade metamorphism (greenschist facies) was accompanied by the development of actinolite from pyroxene; subsequent amphibolite facies metamorphism saw the development of an alkali-rich, blue-green hornblende. The chemical changes in the amphiboles are a succinct illustration of those found in progressive regional metamorphism.

scholarly journals Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

2003 ◽  
Vol 75 (3) ◽  
pp. 393-403 ◽  
Author(s):  
Léo A. Hartmann ◽  
João O.S. Santos ◽  
Jayme A.D. Leite ◽  
Carla C. Porcher ◽  
Neal J. Mcnaughton
Keyword(s):  
Ultramafic Rock ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Rio De La Plata ◽  
Metamorphic Evolution ◽  
Río De La Plata ◽  
La Plata ◽  
Shrimp Geochronology ◽  
Facies Metamorphism ◽  
Magnesian Basalt

The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizário ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. This ultramafic rock was re-metamorphosed at 702±21 Ma during a greenschist facies eventM2; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257±12 Ma) and Camboriú Orogeny (~ 1989 Ma) of the Trans-Amazonian Cycle, followed by an orogenic event (702±21 Ma) of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma) corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton.

scholarly journals Zircon U–Pb Dating and Lu-Hf Isotope of the Retrograded Eclogite from Chicheng, Northern Hebei Province, China

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xu Kong ◽  
Xueyuan Qi ◽  
Wentian Mi ◽  
Xiaoxin Dong
Keyword(s):  
Regional Metamorphism ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Metamorphic Event ◽  
Isotopic Data ◽  
Metamorphic Condition ◽  
Eu Anomaly ◽  
Facies Metamorphism ◽  
Eclogite Facies ◽  
Plagioclase Gneiss

We report zircon U–Pb ages and Lu-Hf isotopic data from two sample of the retrograded eclogite in the Chicheng area. Two groups of the metamorphic zircons from the Chicheng retrograded eclogite were identified: group one shows characteristics of depletion in LREE and flat in HREE curves and exhibit no significant Eu anomaly, and this may imply that they may form under eclogite facies metamorphic condition; group two is rich in HREE and shows slight negative Eu anomaly indicated that they may form under amphibolite facies metamorphic condition. Zircon Lu-Hf isotopic of εHf from the Chicheng eclogite has larger span range from 6.0 to 18.0, which suggests that the magma of the eclogite protolith may be mixed with partial crustal components. The peak eclogite facies metamorphism of Chicheng eclogite may occur at 348.5–344.2 Ma and its retrograde metamorphism of amphibolite fancies may occur at ca. 325.0 Ma. The Hongqiyingzi Complex may experience multistage metamorphic events mainly including Late Archean (2494–2448 Ma), Late Paleoproterozoic (1900–1734 Ma, peak age = 1824.6 Ma), and Phanerozoic (495–234 Ma, peak age = 323.7 Ma). Thus, the metamorphic event (348.5–325 Ma) of the Chicheng eclogite is in accordance with the Phanerozoic metamorphic event of the Hongqiyingzi Complex. The eclogite facies metamorphic age of the eclogite is in accordance with the metamorphism (granulite facies or amphibolite facies) of its surrounding rocks, which implied that the tectonic subduction and exhumation of the retrograded eclogite may cause the regional metamorphism of garnet biotite plagioclase gneiss.

scholarly journals The Coulon deposit: quantifying alteration in volcanogenic massive sulphide systems modified by amphibolite-facies metamorphism

2016 ◽  
Vol 53 (12) ◽  
pp. 1443-1457 ◽  
Author(s):  
Lucie Mathieu ◽  
Rose-Anne Bouchard ◽  
Vital Pearson ◽  
Réal Daigneault
Keyword(s):  
Mass Balance ◽  
Massive Sulphide ◽  
Amphibolite Facies ◽  
High Grade ◽  
Bay Area ◽  
Volcanogenic Massive Sulphide ◽  
High Grade Metamorphism ◽  
And Performance ◽  
Superior Craton ◽  
Ore Zones

The Coulon deposit is a volcanogenic massive sulphide (VMS) system in the James Bay area, Superior craton, Quebec, that was metamorphosed to amphibolite-facies conditions. The chemistry and mineralogy of the VMS-related alteration halo proximal to the mineralized sulphide lenses are investigated, using samples collected in the field and 5583 chemical analyses provided by Osisko Ltd. Alteration is quantified using mass balance and normative calculations, and the application and performance of these methods in an exploration context are investigated. In VMS systems, altered rocks proximal to the ore zones are characterized by multi-element metasomatism, which is best quantified by mass balance methods that have been successfully applied in the study area. However, mass balance calculations necessitate the documentation of a precursor, which is not always possible in an exploration context; therefore, an alternative method (i.e., alteration indices) was also evaluated. In most VMS systems, proximal alteration is characterized by chlorite (chloritization), muscovite (sericitization), and quartz (silicification), while at the Coulon deposit, altered rocks contain mostly cordierite, biotite, sillimanite, and quartz. Alteration indices were calculated using observed and normative minerals, and provide satisfactory results similar to those obtained with mass balance calculations. Using these results, recommendations are made to estimate the intensity of alteration in the core shack using the proportions of observed minerals. Alteration indices are sensitive to the composition of precursors; and because of high-grade metamorphism, chloritization and sericitization are not precisely quantified. Recognizing these limitations is essential to successful quantification of alteration in areas metamorphosed to high-grade conditions.

Rapid fluid-driven transformation of lower continental crust associated with thrust-induced shear heating

2020 ◽  
Author(s):  
Bjørn Jamtveit ◽  
Kristina G. Dunkel ◽  
Arianne Petley-Ragan ◽  
Fernando Corfu ◽  
Dani W. Schmid
Keyword(s):  
Regional Metamorphism ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Source Rocks ◽  
Granitic Rocks ◽  
Time Interval ◽  
Fluid Infiltration ◽  
Facies Metamorphism ◽  
Shear Heating ◽  
Host Rocks

<p>Caledonian eclogite- and amphibolite-facies metamorphism of initially dry Proterozoic granulites in the Lindås Nappe of the Bergen Arcs, Western Norway, is driven by fluid infiltration along faults and shear zones. The granulites are also cut by numerous dykes and pegmatites that are spatially associated with metamorphosed host rocks. U-Pb geochronology was performed to constrain the age of fluid infiltration and metamorphism. The ages obtained demonstrate that eclogite- and amphibolite-facies metamorphism were synchronous within the uncertainties of our results and occurred within a maximum time interval of 5 Myr, with a mean age of ca. 426 Ma.  Caledonian dykes and pegmatites are granitic rocks characterised by a high Na/K-ration, low REE-abundance and positive anomalies of Eu, Ba, Pb, and Sr. The most REE-poor compositions show HREE-enrichment. Melt compositions are consistent with wet melting of plagioclase- and garnet-bearing source rocks. The most likely fluid source is dehydration of Paleozoic metapelites, located immediately below the Lindås part of the Jotun-Lindås microcontinent, during eastward thrusting over the extended margin of Baltica. Melt compositions and thermal modelling suggest that short-lived fluid-driven metamorphism of the Lindås Nappe granulites was related to shear heating at lithostatic pressures in the range 1.0-1.5 GPa. High-P (≈2 GPa) metamorphism within the Nappe was related to weakening-induced pressure perturbations, not to deep burial. Our results emphasize that both prograde and retrograde metamorphism may proceed rapidly during regional metamorphism and that their time-scales may be coupled through local production and consumption of fluids.</p>

TETGAR_C: a three-dimensional (3D) provenance plot and calculation tool for detrital garnets

2020 ◽  
Author(s):  
Wolfgang Knierzinger ◽  
Michael Wagreich ◽  
Eun Young Lee
Keyword(s):  
Three Dimensional ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Igneous Rocks ◽  
Source Rocks ◽  
Accurate Assessment ◽  
Potential Source ◽  
Metaigneous Rocks ◽  
Silicate Rocks

<p>We present a new interactive MATLAB-based visualization and calculation tool (TETGAR_C) for assessing the provenance of detrital garnets in a four-component (tetrahedral) plot system (almandine–pyrope–grossular–spessartine). The chemistry of more than 2,600 garnet samples was evaluated and used to create various subfields in the tetrahedron that correspond to calc-silicate rocks, felsic igneous rocks (granites and pegmatites) as well as metasedimentary and metaigneous rocks of various metamorphic grades. These subfields act as reference structures facilitating assignments of garnet chemistries to source lithologies. An integrated function calculates whether a point is located in a subfield or not. Moreover, TETGAR_C determines the distance to the closest subfield. Compared with conventional ternary garnet discrimination diagrams, this provenance tool enables a more accurate assessment of potential source rocks by reducing the overlap of specific subfields and offering quantitative testing of garnet compositions. In particular, a much clearer distinction between garnets from greenschist-facies rocks, amphibolite-facies rocks, blueschist-facies rocks and felsic igneous rocks is achieved. Moreover, TETGAR_C enables a distinction between metaigenous and metasedimentary garnet grains. In general, metaigneous garnet tends to have higher grossular content than metasedimentary garnet formed under similar P–T conditions.</p>

Mineralogy and genesis of calc-silicates associated with Archean volcanogenic massive sulphide deposits at the Manitouwadge mining camp, Ontario

1992 ◽  
Vol 29 (7) ◽  
pp. 1375-1388 ◽  
Author(s):  
Yuanming Pan ◽  
Michael E. Fleet
Keyword(s):  
Regional Metamorphism ◽  
Spatial Association ◽  
Volcanic Rocks ◽  
Granulite Facies ◽  
Massive Sulphide ◽  
Sea Floor ◽  
Massive Sulphide Deposits ◽  
Volcanogenic Massive Sulphide ◽  
Reducing Environment ◽  
Sulphide Deposits

Skarn-like calc-silicate rocks are reported in spatial association with the Archean Cu–Zn–Ag massive sulphide deposits at the Manitouwadge mining camp, Ontario. Calc-silicates in the footwall of the Willroy mine occur as matrix to breccia fragments of garnetiferous quartzo-feldspathic gneiss and as lenses within garnetiferous quartzo-feldspathic gneiss and are composed of clinopyroxene, garnet, calcic amphiboles, wollastonite, plagioclase, K-feldspar, epidote, quartz, calcite, magnetite, and minor sulphides. Calc-silicates within the main orebody of the Geco mine are characterized by clinopyroxene, calcic amphiboles (Cl–K-rich hastingsitic and ferro-edenitic hornblende, ferro-edenite (up to 4.7 wt.% Cl); and ferroactinolite (6.7 wt.% MnO)), garnet, epidote (including an epidote rich in rare-earth elements and Cl), calcite, quartz, and abundant sulphides. Calc-silicates within the basal 4/2 Copper Zone of the Geco mine contain garnet, gahnite, sphalerite, ferroactinolite (8.5 wt.% MnO), epidote, quartz, biotite, plagioclase, chlorite, muscovite, K-feldspar, and pyrosmalite (with Mn/(Mn + Fe) ratio ranging from 0.21 to 0.61, and up to 3.9 wt.% Cl). The calc-silicates probably represent metasomatic remobilization of dispersed Ca (and Cl) from sea-floor hydrothermal alteration of mafic to intermediate volcanic rocks and are only indirectly related to the hypothesized syngenetic ore-forming processes for the associated base metal sulphide deposits. The calc-silicates formed initially at about 600 °C and 3–5 kbar (1 kbar = 100 MPa) in a mildly reducing environment (from 1 log unit above to 1 log unit below the fayalite–magnetite–quartz buffer) during the upper-amphibolite- to granulite-facies regional metamorphism and were altered subsequently at lower temperatures (<500 °C).

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